Mobile cranes typically include a carrier unit in the form of a transport chassis and a superstructure unit having an extendable boom. The superstructure unit is typically rotatable upon the carrier unit. In transport the crane is supported by the carrier unit on its axles and tires.
At times, the crane needs to be stabilized beyond what can be provided while resting on the tires and axles of the transport chassis. In order to provide stability and support of the crane during lifting operations, it is well known to provide the carrier unit with an outrigger system. An outrigger system will normally include at least two (often four or more) telescoping outrigger beams with outrigger jacks and outrigger pads for supporting the crane when the crane is located in a position at which it will perform lifting tasks.
Utilizing the telescoping outrigger beams, the outrigger pads may be positioned at locations at which they will provide a stabilizing base for the crane. The outrigger jacks are then extended, lowering the outrigger pads into contact with the ground in order to support and stabilize the carrier unit and the superstructure unit. The outrigger jacks may be extended sufficiently, if desired, so as to support the crane in a manner such that the tires are elevated above the ground.
Historically, a crane operator would determine the degree to which the telescoping outrigger beams should be extended to properly stabilize a crane, and visually inspect to determine if the outrigger pads were lowered to a degree such that they were supporting and stabilizing the crane. It is useful, however, to be able to verify that the outrigger pads are actually supporting the crane and to provide an indication to the operator of that status. It would also be beneficial to be able to monitor the loads placed on the outrigger pads and to then provide appropriate signals of those loads to a crane monitoring and control system. Furthermore, it would be useful to be able to use the appropriate signals of those load conditions to determine the stability of the crane.